20 My companion attacks his friends;
he violates his covenant.
21 His talk is smooth as butter,
yet war is in his heart;
his words are more soothing than oil,
yet they are drawn swords.-Psalm 55:20-21, NIV
The shock is real.
You thought you were married to one person, and their behavior is revealing them to be someone else. It is disorienting to put it mildly.
Yes, they could. They did!
Yes, they could live a double life. Yes, they could lie to your face for months (or even years!). Yes, they could steal money. Yes, they could run you down during couples’ counseling and then call their affair partner afterwards.
Your Cheater did this (or whatever your specific experience was). They did this. The sooner that registers the better.
They are counting on you NOT registering this, getting appropriately angry, and setting boundaries to stop their abuse!
Whether this was a “recent” development or through your entire marriage is irrelevant to the present.
It happened.
You need to take action to protect yourself from further damage. And no matter what others may say (or you say to yourself internally), this wicked behavior by your spouse is in no way your fault!